1. Field of the Invention
The present invention relates to a heat exchanger, such as a condenser for use in an automobile air conditioning system, and the assembly thereof.
2. Description of the Prior Art
Japanese Utility Model Application No. 63-142586 discloses a heat exchanger, such as a condenser for use in an automobile air conditioning system as substantially illustrated in FIG. 1.
The condenser includes a plurality of adjacent, essentially flat tubes 10 each having a flat oval cross section and a pair of open ends which allow a refrigerant fluid to flow therethrough. A plurality of corrugated fin units 12 are disposed between adjacent flat tubes 10. The corrugated fin units 12 have a clad construction. Corrugated fin units 12 are brazed to flat tubes 10 to form heat exchange region 100 as discussed below. Heat exchange region 100 allows air to flow therethrough in a perpendicular direction as illustrated by arrow A.
A pair of cylindrical header pipes 120 and 140 each having opposite open ends are disposed perpendicular to both the flat tubes 10 and arrow A. Cylindrical header pipes have a clad construction. The opposite open ends of header pipes 120 and 140 are fixedly and hermetically plugged by respective caps 121, 122, 141 and 142 by brazing. Plate 110, having a generally U-shaped cross section, is fixedly disposed on an upper end of heat exchanger region 100. The ends of plate 110 are fixedly connected to an inside region of an outer peripheral surface of the uppermost portion of header pipes 120 and 140 by brazing. Plate 111, also having a generally U-shaped cross section, is fixedly disposed on a lower end of heat exchange region 100. The ends of plate 111 are fixedly connected to the inside region of an outer peripheral surface of the lowermost portion of header pipes 120 and 140 in the same manner as plate 110. Plates 110 and 111 reinforce the structural strength of the condenser.
Opening 123, having a diameter slightly greater than the outer diameter of cylindrical inlet pipe 22', is formed at an upper portion of header pipe 120. An inlet pipe 22' is provided with an interior portion that is inserted into opening 123 and an exterior portion extending therefrom. The interior portion of inlet pipe 22' is fixedly and hermetically connected to header pipe 120 by a first brazing process. A conventional union joint 23' is provided at an exterior end of inlet pipe 22'. Union joint 23 is fixedly and hermetically connected to inlet pipe 22' by a second brazing process which is done by hand.
An opening (not shown), having a diameter slightly greater than the outer diameter of cylindrical outlet pipe 32', is formed at a lower portion of header pipe 140. Inlet pipe 32' is provided with an interior portion that is inserted into the opening and an exterior portion extending therefrom. The interior portion of outlet pipe 32' is then fixedly and hermetically connected to header pipe 140 in the same manner as inlet pipe 22' is connected to header pipe 120. A conventional union joint 33' is provided at an externally end of outlet pipe 32'. Union joint 33' is fixedly and hermetically connected to outlet pipe 32' in the same manner as union joint 23'. The exterior portions of inlet pipe 22' and outlet pipe 32, protrude from header pipes 120 and 140, respectively, in opposite directions. Inlet pipe 22' and outlet pipe 32' protrude in a plane perpendicular to the flow of air through heat exchange region 100.
Referring to FIGS. 2 and 3, union joint 33' includes hexagonal prism section 331 and cylinder section 332. As illustrated in FIG. 2, cylinder section 332 axially projects from a detail end surface of hexagonal prism section 331. Male screw portion 332a is formed generally along the entire length of an outer peripheral surface of cylinder section 332. Union joint 33' is provided with circular hole 333 axially and centrally bored therethrough. Circular hole 333 includes large diameter portion 333a and small diameter portion 333b which is concentric with large diameter portion 333a. The large diameter portion 333a of circular hole 133 is open at a proximal end surface of hexagonal prism section 331. The small diameter portion 333b of circular hole 333 is open at the distal end surface of cylinder section 332. A boundary between large diameter portion 333a and small diameter portion 333b is located inside of hexagonal prism section 331 near the distal end of hexagonal prism section 331. Annular ridge 334 is formed at the boundary. An inner diameter of large diameter portion 333a is slightly greater than an outer diameter of outlet pipe 32'.
The construction of union joint 23' is identical to the construction of union joint 33'. Therefore, an explanation of the construction of union joint 23' is omitted.
The flat tubes, fin units, header pipes, caps, plates, and inlet and outlet pipes are all temporarily assembled with one another, at the same time in preparation for the first brazing process. After the temporary assembly process is completed, the above elements are transported from an assembly line to a furnace so as to braze the above elements together as described above.
After the first brazing process is completed, the exterior ends of inlet and outlet pipes 22' and 32' are temporarily connected to union joints 23' and 33, respectively, and are then fixedly and hermetically connected to one another in the second brazing process. The manner of temporarily connecting the exterior end of outlet pipe 32' to union joint 33' is identical to the manner of temporarily connecting the exterior end of inlet pipe 22' to union joint 23'. Therefore, only the manner of temporarily connecting the exterior end of outlet pipe 32' to union joint 33' is representatively described below.
A process of temporarily connecting the exterior end of outlet pipe 32' to union joint 33' is carried out in the following manner. First, the exterior end portion of outlet pipe 32' is inserted into large diameter portion 333a of circular hole 333 until the exterior end surface of outlet pipe 32' contacts annular ridge 334. Since the inner diameter of large diameter portion 333a is slightly greater than the outer diameter of outlet pipe 321, a relative displacement of outlet pipe 32' in large diameter portion 333a may occur before or during the second brazing process. Therefore, in order to prevent the undesirable relative displacement of outlet pipe 331, it is known to use a fastening tool which is temporarily attached to the above half-finished condenser so as to firmly fasten outlet pipe 32' and union joint 33' to each other. The fastening tool is detached from a finished condenser after completion of he second brazing process. However, the steps of attaching the fastening tool to the half-finished condenser and detaching the fastening tool from the finished condenser complicates the manufacturing process of the condenser. Hence, the efficiency of manufacturing the condenser is decreased. In addition, the provision of the fastening tool increases the cost of manufacturing the condenser.
It is also known to utilize a T.I.G. welding (tungsten-insert gas welding) process to temporarily connect outlet pipe 32' to union joint 33' before the second brazing process is carried out in order to prevent the aforementioned defect. However, the T.I.G. welding process requires skilled labor. Hence, the efficiency of manufacturing the condenser is decreased. In addition, the cost of the T.I.G. welding apparatus increases the manufacturing costs of the condenser.